I think it was thoughtful of Barry to note that the poll might be skewed by likelihood of response.
I'd like to see a much more granular exploration of those who were affected, as I'm thinking that the poll may also be skewed by types of sites and types of SEOs.
I'm suspecting in many cases that upstream link sources have gotten hit... and I'm guessing that the further away from the SEO industry the link sources were, the less likely it is that they were "tainted". This is completely gut level... I haven't done the kind of study necessary to be more sure of the causes than this educated guess... but from what I've been seeing, there haven't been many surprises.